The present invention relates to reclosable and reopenable thermoplastic film pouch closures and specifically to a structure rendering such a pouch substantially leak resistant. Pouch closures, often referred to as zippers, consist of a pair of extruded thermoplastic strips having longitudinal engagable profiles adapted to be attached along the opening of a pouch forming a marginal portion thereon. The zipper strips are affixed to film stock in the manufacture of plastic bag or pouch flexible containers as disclosed in U.S. Pat. No. 4,698,118. The terms bag and/or pouch are often interchanged in casual speech, however, knowledge of basic differences and purposes of each type is essential to understanding the intended application of the present invention.
Bags are generally constructed of homogeneous heat sealable film stock such as polyethylene or polypropylene where two side walls are fused together at the edges forming a weld approximately 10 times wider than the side wall thicknesses. Zipper strips may be affixed concurrently with extruded film as integral marginal portions of such side walls as disclosed in U.S. Pat. No. 3,462,332. Bags confine goods requiring only moderate protection from ambient conditions such as dust, water droplets and the like. Bags of this construction are less costly to produce than other more complex reclosable flexible containers.
Pouches are generally constructed of composite or barrier film stock where two side wall peripheries are affixed together by one or more of the following methods, i.e. fusing, adhesive bonding, or crimping, which form a face seam seal approximately 100 times wider than the side wall thicknesses. Zipper strips may be affixed to the film stock in preparation of a reclosable plastic pouch such as in U.S. Pat. No. 4,976,811. A pouch protects contents such as food products, pharmacal, chemicals and other substances or goods from deterioration and atmospheric interaction. Pouches of this type are more costly to produce than said bags due to the complexity of the film and the perfection of the face seals needed to provide a higher level of content protection. Zipper strip profiles include interlocking rib and groove elements configured to engage when pressed together in a longitudinal motion and to disengage by pulling the elements in opposite directions at any point along the zipper strips, another form of strip profiles having interlocking clasp and hooked rib elements operates similarly as disclosed in U.S. Pat. No. 4,736,451.
While variations in profile proportions can be seen in the above mentioned forms of plastic bag or pouch zippers, typically such zippers join together with locking elements only, portions or elements exclusively configured to provide a sealing means are not described. A problem exists in that such zipper locking elements when engaged have the appearance of an air tight seal, however contact between the elements is not constant and predictable, and repeated opening and closing of a pouch zipper can cause the locking elements to deform and relax becoming unstable and increasingly less able to hold the strips together tightly, thereby permitting gases or liquids to pass around both strip profiles allowing possible leakage or contamination of the contents within a pouch.
The present invention is unlike the above mentioned prior art, and is distinguishable by the separation of the sealing function from the locking elements thereby providing a distinct sealing means as disclosed herewith.